Technical Field
The present disclosure relates to the technical field for producing a polyether polyol, and particularly to a method for producing a target polyether polyol through an intermediate-target polyether polyol in a continuous reaction cycle inducted by a double metal cyanide (DMC) catalyst and an acid promoter.
Related Art
At present, the common production method of polyether polyol with a DMC catalyst may involve a low molecular-weight alcohol, for example, propylene glycol (diol) or glycerol (trial) as a starter compound to react with a propylene oxide or a mixture of propylene oxide and ethylene oxide in the presence of an ordinary base catalyst such as potassium hydroxide. An intermediate-target polyether polyol in the form of a dihydroxy compound or a trihydroxy compound with a low molecular weight in the range of 400 or 600 respectively may be obtained during the reaction. The low molecular-weight polyether polyol is then subject to a series of complex processes such as neutralization with phosphoric acid, dewatering by adsorption with an adsorbent and filtering, during which about 2% polyether polyol may be lost, causing great environment concerns. Meanwhile, the low molecular-weight polyether polyol prepared with a base catalyst may have a heavy odor due to a high degree of unsaturation, and thus the final product prepared therewith may have the same obvious odor. The low molecular-weight polyether polyol may be degassed and dewatered at a certain temperature, and react with propylene oxide or a mixture of propylene oxide and ethylene oxide in the presence of a DMC catalyst to form the target product, where the induction time may be generally in the range of ten minutes to 1 hour or longer.
Patent No. CN97192141.5 discloses a method for preparing a polyether polyol in the presence of a DMC catalyst by continuously adding an initiating material. The process of continuously adding the initiating material is unstable and may easily cause the catalyst to be inactivated. The inactivated catalyst may be difficult to be further inducted, causing the whole reaction to fail to proceed forward. Moreover, the target product obtained from the final reaction may have a heavy odor, and a wide molecular-weight distribution (either weight average molecular weight or number average molecular weight). Therefore, the practical application for this process is difficult.
Further, during the reaction process, propylene glycol and alkylene oxide are added to the reaction system together and the addition is terminated at the same time. The reaction is stopped once the feed of both materials is terminated, which directly affects the molecular weight distribution and hydroxyl value of the target product.
Patent No. CN03155029.0 discloses a method using a reactive initiating mixture. The target polymer produced from the method has a low molecular weight, and thus the method cannot be used in the production of a long-chain polyether. Furthermore, the low molecular-weight alcohol is not added continuously in the method, which leads to a high content of the low molecular-weight alcohol in the reaction system, and results in a relatively long induction time and reaction time.
Patent No. CN200710138709.8 discloses a method for producing a polyether resistant to high water content. The method mainly aims to produce a polyether resistant to high water content, and reduces the influence of water content in the initiating material after reaction. This method is used to directly produce the target polymer, so the yield is low. During the continuous production process, the induction time of the reaction is long. In the example of polyether production, propylene glycol and propylene oxide are added together and terminated at the same time, which causes the target product to have a wide molecular weight distribution (either weight average molecular weight or number average molecular weight), and affects the performance of the target product.
Patent No. CN201010217182.X discloses a method for producing a short-chain polyether polyol with a starter compound having ultra-low water content in the presence of a DMC catalyst. The product formed by the method is a short-chain polyether polyol with limited applications owing to that the starter compound is a low molecular-weight alcohol having less than 500 ppm of water. Moreover, the method cannot be used in the production of a long-chain polyether polyol. Further, the short-chain polyether polyol produced during the reaction process requires post-processing, which greatly increases the discharge of solid and/or liquid waste from the reaction and the production cost. In some examples, glycerol and propylene oxide are continuously and simultaneously added, which causes the product to have a wide molecular weight distribution.
Patent No. CN201280015084.5 discloses a method for producing a short-chain multi-functional polyether polyol by using a super acid and a DMC catalyst. The target product is a short-chain multi-functional polyether polyol obtained from a starter compound with a low molecular weight. The starter compound contains 3 to 9 hydroxyl groups and excludes the use of monohydric alcohol and dihydric alcohol. Meanwhile, the method involves propylene oxide and a low molecular-weight starter compound such as glycerol being fed into the reactor at the same time, which causes the reaction rate to slow down, and the reaction may terminate prematurely.
In contrast, the present disclosure uses a low molecular-weight polyether initially prepared with a base catalyst as an initiator. For example, the initiator may be a polyether diol or triol having a molecular weight in the range of 400 or 600. An amount of DMC catalyst is added into the process to induct the reaction. Propylene glycol or glycerol and propylene oxide or a mixture of propylene oxide with ethylene oxide are then proportionally introduced into the reaction. A portion of the reaction product is removed and, in the meantime, the DMC catalyst is supplemented such that the amount of the DMC catalyst in the target product is maintained at a specific amount, for example 30 ppm. At a certain temperature and with almost no induction time, propylene oxide or a mixture of propylene oxide with ethylene oxide is introduced into the reaction to achieve the final molecular weight. For example, a polyether diol as a final product generally has a molecular weight of 1000, 2000, or 4000, and a polyether triol generally has a molecular weight of 3000. However, the final molecular weight is not limited thereto.